Internal combustion engine



INTERNAL COMBUSTION ENGINE Filed Feb. 1, 1966 ZSheets-Sheet 1 j/di 16 174 Feb. 20, 1968 I J. 5. CAMPBELL 3,369,530

INTERNAL COMBUSTION ENGINE Filed Feb. 1, 1966 2 Sheets-Sheet 2 HOT GASIFIER HOT GASIFIERWITH LEAKAGE 7 TURBOCHARGED 7 STANDARD GASIFIER I 20 4o BOOST PRESSURE (GAUGE) "overuH of VGI'IOLLS arrangements COMPOUND ENG! N INVENTORO j 0 PATENT AGENT United States Patent Ofitice 3,363,530 Patented Feb. 20, 1368 3,369,530 INTERNAL COMBUSTION ENGINE James S. Campbell, 181 Alwington Place, Kingston, Ontario, Canada Filed Feb. 1, 1966, Ser. No. 524,100 Claims priority, application Canada, Jan. 10, 1966,

349,52 Claims. (Cl. 123-46) ABSTRACT OF THE DISCLOSURE A free piston gasifier having an open ended cylinder and a pair of opposed piston with confronting crowns in the cylinder. The piston crowns and the cylinder, which define a combustion chamber, have vacuum pockets formed therein for thermally insulating the combustion chamber to reducing heat flow from the combustion chamber.

This invention relates to an internal combustion machine, and more particularly, to a free piston type gasifier.

A relatively high proportion of the inefficiency of a piston type engine can be attributed to the heat flow from the combustion chamber through the cylinder walls and the piston. In the case of a free piston gasifier where the hot exhaust gases are utilized to drive an accompanying turbine, the heat loss from the combustion chamber of the gasifier is of even more significance since this represents a loss of energy, a major portion of which could, if maintained in the exhaust gases, be extracted by the turbine.

Thus, it is an object of the present invention to provide a gasifier having a low rate of heat flow from the combustion chamber.

According to the present invention, there is provided a machine having a combustion cylinder member providing a wall defining in part a combustion chamber, and a piston member reciprocably mounted in the cylinder member, and having an end wall forming a piston crown defining in part the combustion chamber. At least one of the members, i.e., the combustion cylinder member and/or piston member, defines a sealed vacuum pocket juxtaposed the wall thereof for thermally insulating the combustion chamber.

More specifically, the machine of the present invention is a free piston type gasifier having a pair of opposed piston members.

In a preferred embodiment of the invention, each piston member is formed by a hollow cylindrical member closed by the crown forming end wall and another wall spaced from said end wall along said hollow cylinder and defining the vacuum pocket therebetween.

Preferably, the combustion cylinder member includes a liner member forming the cylinder wall, and the pocket is defined between a pair of annular spaced wall members encompassing the liner.

Reference is now made to the accompanying drawings, which illustrate the invention as follows:

FIGURE 1 is a longitudinal cross-section view of one example of a gasifier according to the present invention, the right hand portion of the gasifier being omitted for the sake of simplicity; and

FIGURE 2 is a graph showing estimated efficiences offered by the gasifier of the present invention as compared to other types of engines.

In the following description and the accompanying drawings, like reference characters are used for like elements, the reference character 1 generally denoting in the drawing a free piston type gasifier according to the present invention. The gasifier includes a combustion cylinder member 2 providing a cylindrical wall 3 encompassing a combustion chamber 4. Reciprocably mounted within the cylindrical wall 3 is a pair of opposed piston members 5, 5 each of which have end walls 6, 6 forming piston crowns 7, 7 on the piston members. Combustion cylinder member 2 and the piston members 5, 5 have formed therein sealed vacuum cavities or pockets 8c and 8p juxtaposed the cylindrical wall 3 and end walls 6, 6, respectively, for thermally insulating the combustion chamber.

The combustion cylinder member includes a liner member 10 which must be, of course, of high temperature alloy. The liner member 10 midway between its ends has a small opening 11 which receives a nozzle 12 of a fuel injector unit 13 of a well known type. The injector unit 13 is arranged to spray fuel into the combustion chamber 4 substantially when the two piston members 5, 5 approach the inner end of their strokes as is known practice in a two cycle compression ignition engine. Near one outer end of the liner member 10 is a ring of openings or air inlet ports, one of which is shown at 14, about the combustion chamber. These ports are arranged to be uncovered as the piston member 5 at the left side of the drawings reaches the outer end of its stroke to permit compressed air to enter the combustion chamber from a manifold 15. On the opposite side of opening 11 as ports 14 is a similar series of exhaust ports (not shown) arranged to be uncovered by the piston member 5 on the right hand side of the drawing, as it moves towards the outer end of its stroke. The era haust ports are in communication with a gas turbine by means (not shown), whereby the hot exhaust gases flow ing from the combustion chamber 4 drives the turbine.

The pockets 8!: in the combustion cylinder member 2 are preferably formed by a casing or outer member 16 fabricated from a number of parts to provide a pair of annular spaced walls which define the pockets therebetween and encompass the liner member 11, the outer member 16 in fact being made up prior to the insertion of the liner member 11. The outer member 16 firstly includes a pair of concentrically disposed cylindrical members 17 and 18 both of which have an opening in which is welded a fitting 20 mounted for injector unit 13. As the fitting 20 is connected'in the openings in the cylindrical members 17 and 18 by welds'23 and 24, the space between the members 17 and 18, namely pocket 86 is not exposed to the atmosphere via the openings. As shown in FIGURE 1, the left hand end of cylindrical members 17 and 18 are joined by welds 2S and 26, to axially extending, annular flanges 21 and 22 of corresponding diameters on manifold 15. The opposite ends of the cylindrical members 16 and 17 are similarly joined to an exhaust manifold 19. By forming the welds 23, 24, and 25, 26 and the corresponding welds at the opposite end, or at least the last of these welds to be carried out, in a vacuum by the now frequently utilized electron beam welding process, it is possible to close the pocket 80 in an evacuated state, and as the vacuum pocket 80 remains hermetically sealed by the welds heat flow from cylindrical member 17 to cylindrical member 18 is impeded. Thus, as the heat is substantially prevented from leaving liner member 10 through the combustion cylinder member 2, the temperature within the combustion chamber 4 is maintained at a higher level which results in a higher exhaust gas temperature.

The gasifier has at each end thereof an air compressor 30 and a bounce chamber 31, and as these components at opposite ends of the gasifier are substantially identical, only the left hand portion of the gasifier has been shown in the drawings. The bounce chamber 31 includes a liner 32 which is axially aligned with the liner member 10* of the combustion chamber 4. The liner 32 is mounted within an extension 33 of a member 34 which also forms the head of the compressor 30. The bounce chamber 31 is closed at its outer end by a head member 35 which is connected to extension 33 by bolts 36, one of which is shown in the drawings. Head member 35 is provided with a threaded opening 37 to which means well known in the art may be connected for controlling the bounce pressure in the chamber. Passages 38 may be provided between the liner 32 and extension 33 for coolant so that temperature of the bounce chamber may be controlled.

Each piston member has an elongated hollow portion 40, one end of which is formed integrally with the end wall 6. An inner end 41 of the piston member 5 reciprocably carried in the liner member of the combustion chamber 4 is of a different, diameter than an outer end 42 in the bounce chamber, and thus a circumferential shoulder 44 is provided between the ends of the piston member 5. The inner end 41 is a close fit within the liner member 10 and instead of having conventional type rings it is provided with a plurality of closely spaced, circumferential labyrinth forming grooves45 therearound. Sealing is similarly accomplished in the bounce chamber between the outer end 42 of piston member 5 and liner 32 by grooves 46.

- The outer end 42 of piston member 5 within the bounce chamber 31 is closed by wall or end plate 50 which is joined to the elongated hollow portion 40 to thereby provide a completely closed member. The end plate 50 is welded in place by a weld 51 to hermetically seal the pocket withinthe piston member 5, the welding being carried out by an electron beam process as previously described to capture a vacuum within each piston member 5 so that in operation substantially no heat from the combustion chamber 4 can escape through the crowns 7, 7.

In combustion cylinder member 2 at each end of liner member 10 is an annular bearing member which reciprocably receives inner end 41 of the piston member 5. This piston guiding bearing member is retained in place by a retainer ring 56. The outer end 42 of piston member 5 is similarly guided in an annular bearing 57 held adjacent the inner end of the bounce chamber liner 32 by a retainer ring 58.

As shown in FIGURE 1, the outer end of the combustion cylinder member 2 is actually formed integrally with end member 60 of compressor 30. This end member 60 has opening receiving the outer end of liner member 10 and the bearing member 55 and is provided with spaced annular flanges 61 and 62 which match'with annular flanges 63 and 64 on the opposite side of manifold 15 as flanges 21 and 22. Flanges 61 and 63 and flanges 62 and 64 are joined by welds 65 and 66, respectively, these welds, like the previously discussed welds being carried out by an electron beam welding process, in order that auxiliary vacuum pocket 80 outward of the manifold 15 can be provided. to even further thermally insulate combustion chamber 4 from the surroundings.

End member 60 of the air compressor 30, which is situated in the gasifier 2 between the combustion chamber 4 and bounce chamber 31, is secured to head member 34 of the air compressor by a plurality of studs and nuts, one set of which is shown at 70. Clamped between head member 34 and end member 60 is a compressor liner 71 which defines the compressor cylinder 72 concentrically encircling piston member 5. A coolant jacket 73 similarly is held between members 34 and 60 and engages the outer surface of liner 71, A ringed compressor piston 74 is carried by piston member 5 within compressor cylinder 72, and as shown, is fixed thereto for reciprocation therewith by being clamped between shoulder 44 and a nut member 75 screwed into a threaded portion 76 on piston member adjacent shoulder 44.

Head member 34 carries an inlet valve 77 in the side of cylinder 72 which permits air to be drawn into the compressor cylinder 72 from atmosphere as piston member 5 is bounced through its return stroke. The valve 77 is a one-way valve which closes as soon as the power stroke commences so that air is trapped in compressor cylinder 72 and is compressed by piston 74. Head member 34 is further provided with a plurality of one-way outlet valves 78 in the end of cylinder 72 about piston member. These outlet valves 78 permit flow of the air compressed in cylinder 72 on the power stroke of piston member 5 out into an annular chamber 81. From chamber 81, the compressed air flows through a duct 82 in communication with chamber 81 to manifold 15 and then into the combustion chamber 4 through ports 14 as piston member 5 approaches the outer end of its power stroke as indicated by the arrows in FIGURE 1. Manifold 15 also receives compressed air from the compressor which is at the opposite end of the gasifier 2 and is identical to the one just described, through a second duct 83.

Although the manner in which each piston member 5 is maintained within the. gasifier 2 is ancillary, it is not insignificant. For example, the design permits selection of the desired area of bounce piston completely independent of the diameter of the piston within the combustion chamber. The design of the bounce chamber in conjunction with the manner in which the bearing members 55 and 57 support the piston member 5 is also. important in that it allows small clearance, between the piston members and the liners, which small clearances can be effectively sealed by the labyrinths described.

As is obvious, it is possible to provide the vacuum pockets only in the piston members 5, 5 or in the combustion cylinder member 2 and still achieve the benefit of increased efficiency. However, the more perfect the insulation provided by the vacuum pockets the better the efficiency of the machine. Moreover, although the invention has been described in connection with a gasifier, features of the present invention may be also utilized in a crankshaft type engine. However, in crankshaft type engines the improved efficiency is not as significant since in the case of a gas generator in combination with a turbine increased efliciency is due to (1) improved diesel efficiency leading to increased compressor work, i.e., higher mass flow for a given diesel input, and (2) increased exhaust temperature due to reduction of heat loss from the diesel cylinder, the crankshaft type engine does not benefit thermodynamically from the higher temperature of the exhaust gas unless a turbosupercharger is used in conjunction with the engine. One other fact, which makes the present invention more practical for free piston gasifiers such as that shown in FIGURE 1 rather than a crankshaft type engine, is that the piston members are substantially free from side thrust, and because no external kinematic linkage is attached to the piston members 5, 5, the piston members lend themselves to a ringless construction utilizing the described labyrinth forming grooves.v

even a series of such walls may be provided, closer to the end wall 6 so that a much shorter vacuum pocket, or

series of vacuum pockets, is provided within the piston at the crown end thereof.

In addition to improving the efficiency the vacuum pockets in the pistons may otherwise. benefit from the engine design by reducing the stresses in the crown of the pistons. For example, the mean piston temperature of a highly supercharged diesel engine developing 250 p.s.i. B.M.E.P. at a boost pressure ratio of 4, and employing piston cooling is of the order of 450-500 C. at the centre of the crown. Depending on crown thickness, the temperature gradient throughthe crown is on the order of ZOO-250 C. Accordingly, the resultant stresses, consisting of pressure and thermal stresses, are, therefore, very high. When the heat flow through the piston is prevented by the vacuum pocket withinthe piston, the general temperature level of the piston crown will approximate to the mean gas temperature, which with a maximum gas temperature of the order of 2500" C., would be in the range of 800-1000" C. Since heat transfer through the crown is substantially eliminated, the thermal stresses are greatly reduced. However, it is obvious that the material selected for the pistons would have to be of a high-temperature alloy capable of withstanding the working stresses under the increased working temperature.

The gas thermal efficiency for a gasifier arrangement 1 is predicted from estimated component efficiencies, valve and port pressure drops, and fractional cylinder heat loss from the following expression:

H =Overall fractional heat loss m=Diesel indicated efl'iciency n =verall mechanical efiiciency n =Compressor isentropic efficiency F=Pressure loss factor P,,=Atmospheric pressure P =Turbine inlet pressure The potential gains may thus be calculated and compared with a standard gasifier arrangement and are illustrated in a comparable form in the graph shown in FIG- URE 2. The graph shows H as equal to 0 as a limiting case and a corrected curve which was calculated by using a step-by-step analysis of leakage past the labyrinth and other thermodynamic corrections. Also plotted on the graph are curves showing the efficiencies of two other types of engines, namely a turbocharged engine and a compound engine, the latter being one in which part of the crankshaft output power is used to assist an exhaust gas turbine in driving a compressor for the incoming air to the engine. It is believed apparent that the present invention as shown in the graph raises the efficiency of a gasifier arrangement an amount which is significant particularly when it is considered that at higher boost'pressures, efficiencies are possible well above the efficiencies of other engines in the same class.

Even further insulation of the combustion chamber 4 can be obtained by polishing or otherwise plating or treating the surfaces of parts about the combustion chamber 4, such as the internal surfaces of the walls defining the vacuum pockets 8c and 8p, so that emitted radiant heat is reflected back towards the combustion chamber. For example, inner surface 40a of portion 40 and inner surface 50a of end plate 50 of each piston 5 may be highly polished so that heat radiated from the crown 7 is reflected back and its escape from the vicinity of the combustion chamber is thereby impeded. Similarly, the inner surface 18a of cylindrical member 1'8 may also be of reflective character so that radial heat is turned back towards the combustion chamber 4. Furthermore, inside surface 6a in the pocket 8p of each piston member 5 and the outer surface 17a of cylindrical member 17 in pocket 8c may be dull and dark to form a heat absorptive surface. Thus, heat reflected by surfaces 40a, 50a and 18a is more readily imbibed back into the combustion chamber 4 from pockets 8p and 8c.

The embodiment shown and described above is, of course, only one example of the present invention, it being possible to incorporate other modifications Without departing from the spirit of the invention as defined in the appended claims.

I claim:

1. A free piston gasifier comprising a combustion cylinder member having an open ended cylindrical wall encompassing a combustion chamber, and a pair of opposed piston members reciprocably mounted in said cylinder member and each having an end wall forming confronting piston crowns on said piston members, at least one of said members having formed therein a sealed vacuum pocket juxtaposed the wall thereof for thermally insulating said combustion chamber.

2. A. gasifier as defined in claim 1, wherein each piston member is formed by a hollow cylindrical member closed by said end wall and another wall spaced from said end wall along said hollow cylinder and defining the vacuum pocket therebetween.

3. A gasifier as defined in claim 1, wherein said combustion cylinder member includes a liner member forming said cylinder wall, and wherein said pocket is defined between a pair of spaced, coaxial wall members encompassing said liner.

4. A gasifier as defined in claim 3, wherein the outer wall member of the coaxial pair has an inner surface of reflective character for reflecting radiant heat back to said combustion chamber, and wherein the inner wall of the coaxial pair has an outer heat absorptive surface for imbibing the reflected heat back in the combustion chamber.

5. A gasifier as defined in claim 1, wherein said one member has pocket defining surfaces of reflective character for impeding heat radiation from said combustion chamber.

6. A gasifier as defined in claim 5, wherein each of said piston members contains said pocket, and wherein said end wall of each piston member has a dull, dark, heat absorptive surface in the pocket.

7. A gasifier as defined in claim 1, wherein each of said piston members has a plurality of closely spaced, circumferential, labyrinth-forming grooves adjacent the crown thereof.

8. An opposed piston type gasifier comprising an open ended cylinder liner member encompassing a combustion chamber, an outer casing about said liner member and defining at least one hermetically sealed vacuum pocket around and thermally insulating said combustion chamher, and a pair of opposed piston members each having an inner end portion reciprocably mounted in said liner member, said end portions of the piston members having confronting piston crowns closing opposite ends of said combustion chamber, each of said piston members having a hollow configuration adjacent the crown thereof defining a hermetically sealed vacuum pocket for impeding heat flow through the piston member.

9. A gasifier as defined in claim 8, and further comprising a pair of cylinder members aligned with said I combustion chamber, each cylinder member being opposite one end of the combustion chamber and forming a bounce chamber for one of said piston members, and wherein each of said piston members includes an elongated hollow cylindrical member and has a closed outer end portion reciprocably received in one of the bounce chambers.

10. A gasifier as defined in claim 9, wherein the cylindrical member defining each piston member is integrally formed with said crown of the piston member, and wherein the outer end portion of each piston member in the bounce chamber is closed by an end plate welded to said cylindrical member and sealing the vacuum pocket within said hollow cylindrical member between the crown and end plate.

11. A gasifier as defined in claim 10, and further comprising a pair of annular compressor cylinders concentrically disposed about one each of said piston members between the combustion chamber and each bounce chamber, and a pair of compressor pistons disposed one each in the compressor cylinders and fixed one each to the piston members for reciprocation therewith.

12. A gasifier as defined in claim 11, wherein each cylindrical member forming the piston member is stepped from one diameter at the inner end portion to another diameter at the outer end portion to thereby form a circumferential shoulder between opposite ends thereof, and wherein each compressor piston is clamped between said shoulder and a nut member screwed onto a threaded portion about said cylindrical member adjacent said shoulder.

13. A gasifier as defined in claim 11, wherein said cylinder liner member defines an air inlet port for said combustion chamber, and wherein at least one of said compressor cylinders has a compressed air outlet valve in communication with said port,

'14. A gasifier as defined in claim 9, wherein each piston member has a plurality of closely spaced, circumferential, labyrinth forming grooves therearound at both said inner end portion and said outer end portion.

15. A gasifier as defined in claim 9, wherein annular bearing means are provided at opposite ends of cylinder liner members and adjacent said bounce chambers, said 8 bearing means reciprocably receiving and guiding said piston members.

References Cited UNITED STATES PATENTS 762,178 6/1904 MacFadyen 92144 X 1,019,790 3/1912 Heylandt 92144 1,245,641 11/1917 Ver Planck 92-l76 1,390,193 9/1921 Bowmar 92-176 3,145,660 8/1964 Bush 12346 X FOREIGN PATENTS 649,810 1/1951 Great Britain.

WENDELL E. BURNS, Primary Examiner. 

